1. Field of the Invention
The present invention relates to wireless communications. More particularly, the present invention relates to a channel estimation method and apparatus using a self-tracking algorithm for improving channel estimation accuracy.
2. Description of the Related Art
With the standardization and product maturity of high speed mobile communication technologies such as Wideband Code Division Multiple Access (WCDMA) and High Speed Downlink Packet Access (HSDPA), much research has been conducted to develop equalizer-based receivers appropriate for high speed mobile communication. A core structure of the equalizer-based receiver has been introduced that includes a channel estimator and an adaptive equalizer based on the channel estimator. The channel estimator has a tap long enough to receive all the delay profiles of a signal experiencing multipath fading and the adaptive equalization algorithm uses the multi-tap channel values. In the technologies of the related art, the receiver is designed with a long tap length in consideration of the delay profiles of a multi-path channel and a channel estimator having multiple taps that alternate between active and inactive states depending on the channel condition.
The self-tracking channel estimation method of the related art estimates the channel by analyzing properties of a delay profile of a multipath reception channel and changes the positions of the taps of the channel estimator and equalizer in a unit of a fixed chip. However, since the method of the related art controls the slew at the chip rate in a fixed size chip interval, a mismatch of a peak energy position of the received signal and the tap position of the channel estimator and equalizer can cause reception energy loss.
FIGS. 1 to 3 are graphs illustrating a problematic situation in the channel estimation method of the related art.
FIG. 1 shows the channel estimator and equalizer multi-tap energy distribution when the position of a maximum peak position is substantially identical with the reference tap position, according to the related art. FIGS. 2 and 3 show the channel estimator and equalizer multi-tap energy distributions when the maximum peak position is different from the reference tap position due to an energy shift, according to the related art.
Referring to FIG. 1, when the maximum peak of the received signal is substantially identical with the tap position of the channel estimator and equalizer, there is no reception performance loss. However, referring to FIGS. 2 and 3, when the maximum peak of the received signal is different from the tap position of the channel estimator and equalizer, energy loss occurs. Such energy loss may occur when energy distribution of the multipath fading channel shifts in a resolution less than the chip rate resolution. FIG. 2 is a graph showing the result of the shift of the energy distribution of the received signal in a resolution less than the chip rate resolution, according to the related art. In this case, the chip rate slew control method of the related art decides that there is no slew, whereby the channel estimator and equalizer fail to match the maximum peak with the tap position (i.e. fail to detect the maximum peak), thereby resulting in energy loss as denoted by reference numeral 111. FIG. 3 is a graph showing the result of the shift of the energy distribution of the received signal in a resolution greater than the preset chip rate resolution, according to the related art. Since the taps of the channel estimator can operate with the slew at the chip rate in fixed chip size, the maximum peak cannot be matched with any tap when the energy distribution is shifted by as much as greater than the fixed chip size, thereby resulting in energy loss as denoted by reference numeral 113.
As described above, the channel estimation method of the related art can perform tracking to match the maximum peak of the energy distribution of the multipath fading channel with the channel estimator and equalizer taps by adjusting the tap position in a unit of the fixed size chip interval through the chip rate slew control when the energy distribution of the multipath fading channel is shifted. However, when the energy distribution of the multipath fading channel is shifted in a resolution less than the chip rate resolution, the channel estimation method of the related art fails to match the reception point of the maximum peak with the channel estimator and equalizer tap, thereby resulting in energy loss of the received signal.